Means for and method of producing time modulated signal impulses



Oct. 19, 1948. G. GUANELLA ET AL 2,451,824

MEANS FOR AND METHOD OF PRODUCING TIME MODULATED SIGNAL IMPULSES Filed Nov. 22, 194el n 4 sheets-sheet 1 Hym- T1 qi Zik-)I .n h I i IZ? 'l I I v I Il' XZ" 1 n' f' zn n f l .ll/Xl:

ZM i@ ATTORNEY oct. 19, 194s.

TIME MODULATED SIGNAL vIMPULSES Filed NOV. 22, 1946 G. GUANELLA El' AL MEANS FOR AND METHOD OF PRODUCING 4 Sheets-Shget 2 ATTORNEY Oct. 19, 1948. G. GUANELLA Er AL MEANS FOR AND METHOD 0F PRODUCING TIME MODULATED SIGNAL IMPULSES 4 Sheets-Sheet 5 Filed Nov. 22, 1946 vvvvvv w, a SLR R oma@ n Tnm N Nur. R EGTM 0 VV W mmc/ A su @am Y B r. i l l G. GUANELLA ET AL MEANS FOR AND METHOD OF PRODUCING Oct. 19, 1948.

TIME MODULATED SIGNAL IMPULsEs 4 Sheets-Sheet 4 Filed Nov. 22,

1 i E I-Ill I 'I |-Il E I I .mh um l INVENTORS Gusrng Gua/vnl.: BY P401. Gurn/vasi? ATTORNEY Patented Oef. 19, 1948 MEANS FOR AND METHOD OF PRODUCING TIME MODULATED SIGNAL IMPULSES Gustav Guanella, Zurich, and Paul Gttinger, Wettingen, Switzerland, asslgnors to Radio Patents Corporation, New York, N. Y., a corporation of New York Application November 22, 1946, Serial No. 711,538

In Switzerland December 18, 1945 The present invention relates to a novel method of and means for producing time modulated signal impulses used for the transmission of voice,

' telegraphy, facsimile, teletype or any other signals by means of carrier signals, such as radio waves.

Pulse time modulation, like frequency modulation, when used in connection with wireless transmission has the advantage over amplitude modulation of a substantial reduction of interference in the receiver and simplification of the transmitting apparatus. Whereas, however, in frequency modulation, an especially designed receiver is required which cannot be used for the reception of amplitude modulationI pulse time modulation has the advantage that it may be received with either a standard frequency modulation or amplitude modulation receiver. For this reason, pulse time modulation is especially suited for broadcasting purposes, in as much as the standard amplitude modulation receivers may be employed with only slight changes.

As is well known, pulse time modulation involves the generation of a series of current or voltage impulses or high frequency wave trains of constant amplitude the width or duration of which is varied in accordance with the amplitudes of the modulating signal.

An object of the present invention is to provide a greatly simplified and eillcient method of and system for producing time modulated impulses, especially suited for use in connection with carrier wave transmission. The impulses may be in the form of either voltage or current pulses and serve to control a carrier frequency generator, for transmitting corresponding carrier wave trains in a manner well known in the art.

Various methods of producing time modulated impulses from a given modulating signal wave, such as voice, etc., have been proposed in the past, all of which have in common that the time modulation is produced directly from the modulating signals. Such arrangements usually require a considerable amount of apparatus compared with the improved and direct method and apparatus therefore proposed by the invention.

With the above object in view, the invention involves generally the combination of a pair of substantially identical and synchronous auxiliary oscillations or waves, either additively or multiplicatively, and modulation of the phase of at least one of said oscillations or Waves in accordance with a modulating signal to be transmitted. The auxiliary oscillations or waves may be of any desired shape such as sinusoidal or in the form of impulses, that is of either rectangular or trapezoidal shape.

Further objects and novel aspects of the invention will become more apparent from the following detailed description taken in reference to the accompanying drawings forming part of this specification and wherein:

Figures la to lc, Figures 2a to 2c and Figures 3a to 3c are a series of theoretical diagrams illustrative of the novel process of pulse time modulation according to the invention, utilizing rectangular or square waves as auxiliary oscillations;

Figures 4a. and 4b, Figures 5a and 5b and Figures 6a and 6b illustrate an alternative method differing from the previous figures by utilizing a pair of sinusoidal auxiliary oscillations for carrying out the invention;

Figure '7 is a block diagram illustrating a complete pulse time -modulation transmitter constructed in accordance with the principles of the invention;

Figure 8 is a partial diagram showing a phase modulator circuit suitable for use in carrying out the invention;

Figure 9 is a detailed circuit diagram of transmitter according to Figure '7;

Figure 10 is a block diagram similar to Figure 7 illustrating a modified pulse time modulated transmitter in accordance with the invention;

Figure 11 is a detailed circuit diagram of the transmitter shown in Figure 10; and

Figure 12 is a theoretical diagram illustrative of the function of the pulse time modulator according to Figure 10.

Like reference characters identify like parts throughout the different views of the drawings.

In many practical cases, the phase modulation of only one of the auxiliary oscillations or Waves will be suflicient with the frequency of the other wave being maintained constant. However, by subjecting both waves to phase modulation, it is possible to secure an increased total phase deviation or degree of modulation. Of special interest is the case where two alternating current voltages of equal amplitude are phase modulated in an opposite sense such as by means of a ilrst phase modulator acting to effect a leading phase and a second phase modulator effecting an equal and lagging phase variation.

This latter method will be further explained with reference to Figures 1a to lc, 2a to 2c and 3a to 3c where in both alternating voltages are in the form of rectangular impulses or squarewaves. As is understood, the same results will be obtained the from waves of any other shape such as sinusoidal or any other oscillations.

Referring to Figure 1a, there are shown a pair' of rectangular impulses i1 and iz which may be either current or voltage impulses and which are displaced by a predetermined phase difference corresponding to the zero or unmodulated condition and being equal to 90 in the example illustrated. The frequency of the impulses il and iz or the pulse sequence per second are identical, that is the impulses are in synchronism with each other. 'I'he relative time phase position between the impulses, however, varies from the 90 or zero position shown, corresponding to degree modula tion m or instantanous amplitude of a modulating signal. In other words, the mutual time phase position between the impulses changes gradually in proportion to the degree of modulation, as soon as a modulating signal is applied to the generator or transmitter.

Figures 2a and 3a illustrate the relative position of the impulses i1 and i2 for two further modulation conditions. In Figure 2a. the overlapping period of the impulses is less than in Figure 1a that is less than 90 or one quarter of the impulse period. In Figure 3, the overlapping period is shown larger than in Figure 1a. The modulation conditions in Figures 2a and 3a correspond to instantaneous modulation signal amplitudes of opposite sign as is understood.

In accordance with the present invention, the auxiliary oscillations of equal amplitude but relatively varying time phase position are combined or superimposed to derive a resultant single pulse time modulated signal. This combination may be either additive or multiplicative. In Figures lb, 2b and 3b the results of an additive combination of the impulses i1 and i2 and in the corresponding Figures 1c, 2c and 3c the result of a multiplicatlve combination of the impulses i1 and in are shown. These gures demonstrate that. both with additive and multiplicatlve combination, the width of the resultant impulses varies in proportion to the original time phase of the impulses i; and in, i. e. in proportion to the instantaneous amplitudes of a modulating signal. In either case of additive or multiplicatlve combination a pulse time modulated output signal is obtained in this manner. The impulses obtained by additive combination, Figures 1b, 2b and 3b, if rectified, that is with their negative pulses being reversed, result in nal signal pulses substantially identical to those obtained by a multiplicatlve combination, Figures 1c, 2c and 3c. Furthermore, the resultant impulse signals have a frequency twice the original impulse frequency.

In an analogous manner, Figures 4a and 4b, 5a and 5b and 6a and 6b illustrate the conditions of modulation if the auxiliary oscillations or waves are of sinusoidal instead of a square shape, as shown in the preceding illustrations. According to an alternative method, a combination of a sinusoidal and impulse current or voltage may be employed for the purposes of the invention.

Referring to Figure 7, there is shown in block diagram form a complete transmitting arrangement embodying an impulse modulating system constructed according to the principles of the invention and using sinusoidal voltages as auxiliary oscillations. The generator l0 serves to produce an alternating current voltage of a frequency corresponding to the desired impulse frequency. Thus, in the case of voice, the generator frequency may be within 20 to 100 kilocycles. Any other basic or impulse frequency may be used,

depending upon the character of the message or information to be transmitted. The oscillations eo supplied by the generator I0 are simultaneously applied to a pair of phase modulators l`l and I2. The oscillations en' applied to the modulator Il are previously passed through a phase shifter I3 designed to effect a fixed phase rotation of 90. In this manner, a zero or rio-signal modulation condition =90 is obtained as illustrated in Figure 4a. 'Ihe phase modulators Il and I2 are furthermore controlled by the modulating current i; supplied from a suitable input device such as a microphone circuit, facsimile apparatus etc. preceding a low frequency amplier Il.

Accordingly, the time phase position of the output voltages el and er of the modulators il and I'2 is equal to 90 in the no-signal condition, Fig. 4a, that is in the case of the modulating current i4 being equal to zero. With the occurrence of a modulating current i4, the relative time phase between the voltages e1 and er' varies in such a manner that the phase angles of said voltages are changed in an opposite' sense by equal amounts, as shown in Figures 5a and 6a. In this manner, the relative phase between the voltages e1 and e1 is reduced or increased in respect to the normal or 90 phase difference, depending on the degree of modulation or the instantaneous amplitude of the modulating signal. The phase deviations of voltages er and e1' are symmetrical in respect to the zero or no-signal position.

The phase modulated sinusoidal voltages e1 and e1' may be intermodulated directly in a suitable mixer to produce time modulated voltage impulses as shown in Figures 4b, 5b and 6b, which latter upon rectification and amplitude limitation are converted into rectangular or squaretopped and time-modulated impulses, as will readily be understood from the above.

In the example according to Figure 7, the sinusoidal phase modulated voltages e1 and e1' are first applied to suitable amplitude limiters I5 and I6, respectively. In the latter, the original sinusoidal voltages are converted into approximately rectangularly shaped voltages e2 and e2' substantially of the type according to Figures la., 2a and 3a. The latter having a constant amplitude are then applied to the combining device or mixer i8. This mixer may be in the form of a multi-grid electronic mixer tube of known construction. The grid bias voltages applied to the later may be so regulated as to result in either an additive or multiplicatlve combination of the instantaneous voltages ez and e2' according to Figures 1b, 2b and 3b and 1c, 2c and 3c, respectively.

'I'he thus obtained time modulated impulses e: are applied from the mixer I6 to a keying circuit i1 forming a part of the high frequency transmitter. In this keying circuit the oscillations of the high frequency carrier generator I8 are controlled in accordance with the modulation lmpulses ea. The control of the high frequency carrier is such that the high frequency amplitude is varied between zero and maximum directly in accordance with the controlling impulses. The high frequency wave trains thus obtained are further amplled in a power amplifier 20 and may serve to feed an antenna or other carrier transmission channel. If desired, the power amplifier 20 may be omitted and the impulse modulated carrier signals directly applied to the antenna or other signal transmitting channel.

The parts and circuit elements employed in Figure 7 may be of standard and known conof any known type of oscillator suitable to produce a constant oscillating frequency. The phase shifting circuit Il may be composed of a network of induction coils, condensers and resistors in accordance with well known practice. The same applies to the phase modulators II and I2 which in the embodiment as shown in Figure 8 may consist of a pair of amplifier tubes 2| and 22 controlled by the signals eo and en', respectively, and provided with resonant anode circuits tuned to the frequency of the auxiliary generator I0. The phase modulation in the example shown is eifected by the aid of auxiliary windings 2l and 26 of iron-core tuning inductances 22 and 24 of the resonant circuits respectively. The control windings 25 and 28 are energized by the modulating current i4 which causes a variation of the inductive reactances of the resonant circuits, resulting in a corresponding phase variation of the output currents of tubes 2i and 22. The windings 25 and 26 are so connected as to obtain opposite phase variations in the circuits as is understood. Any harmonics produced by the modulation process may be suppressed by means of subsequent filter circuits shown at 21 and 28, respectively.

The amplitude limiters I5 and I9 in Figure 'l may also be of standard construction such as in the form of screen grid tubes operated with suitable bias potentials to effect an amplitude limitation of the voltages e1 and e1 due to grid current flow and resulting in approximate rectangular output waves. in a manner well understood by those skilled in the art.

The mixer I6 is preferably in the form of a vacuum tube having two equally controlled grids designed to be equally effective upon the common plate current. This may be obtained by the provision of a pair of grids of equal dimension wound upon a cylindrical surface in the form of a double helix or spiral. Both grids are s0 biased as to cause a flow of the annode current for positive control potentials only if applied to the both grids.

The power amplifier 2li may be of any design also well known in the art. The keying circuit Il may be in the form of an amplifier stage com prising a tube with a control grid to which is applied the impulse voltage ea, with the grid bias potential so chosen that the high frequency carrier oscillation supplied by the generator Il is controlled between zero and maximum amplitude in accordance with the signal pulses ea supplied by the pulse modulator.

In a simplified arrangement, the keying circuit Ii may be omitted and the control of the high frequency carrier oscillation effected lby directly applying the output voltage of the mixer I0 to the grid of an oscillator tube of the generator I8. The latter is then so operated that with a. positive impulse voltage the oscillations will be started and with a negative impulse voltage the oscillations will be completely suppressed.

Referring to Figure 9, there is shown a complete circuit diagram of a transmitting system of the type according to Figure 7. The auxiliary oscillator Ill is shown in the form of a standard regenerative oscillator tube 25|, the phase shifter I3 consists of a lter made up of a series resistance and a pair of parallel condensers, and the phase modulators II and I2 are substantially similar to those shown in Figure 8. If desired, filter circuits as shown at 21 and 28 in Figure 8 may be provided to eliminate undesirable harof vacuum tubes Il and Il :operated with suitable bias potentials to eect an amplitude limitation in a manner well known. The mixer Il is in the form of a multi-grid electron tube .I2 whilethe amplifier I4 is shown as a standard audio amplifier supplying an amplified modulating current u. l

Referring to Figure 10 there is shown a modi iication of the system according to Figure "L According to this -embodiment the output voltages4 or currents of the modulators II and I2 are applied directly to the mixer Il in which the auxiliary sinusoidal oscillations are combined or inter-modulated as shown in Figures 4b, 5b and 6b. This. mixer4 may be an electronic tube similar to that shown before or it may bein the form of a rectifier bridge known as a ring modulator and effecting o multiplicative mixing or combination of the applied input voltages. As a result, the output voltage e: will have a shape as shown in Figure l2. In the latter the time phase angles ci, qu, representing the points of the lvoltage 4 es passing through the zero axis vary in proporvoltage es ofy substantially rectangular shape and corresponding to Figures 1c, 2c and 3c. The limiters may be either triodes or diodes and the output voltage esmay serve to control the keying circuit of a high frequency transmitter, in substantially the same manner as described hereinabove.

The detailed circuit diagram shown in Figure ll corresponds substantially to Figure 10 with the auxiliary oscillator I0, the phase modulators Il and I2 and phase shifter Il and audio amplifier being substantially of similar construction to those shown in Figure 9. The mixer II in Figure 11 is shown inthe form of a rectifier bridge circuit or ring modulator as mentioned, while the limiters Il and 8l are in the form of a suitably biased ampliiier 31 and a pair of oppositely connected rectiflers Il and 2l, respectively, as explained above.

While the invention has been described with speciilcreference to the embodiments shown in the. drawings, it is understood that various changes in.. the circuits and elements used as well as the substitution of equivalent elements or circuits for those shown and disclosed herein for illustration may be made in accordance with the -broader scope and spirit of the invention. The specification and drawings are accordingly to be 'regarded in an illustrative rather than in a limiting sense.

monies resulting from the modulation process. 1s wavecomprising a series of constant amplitude aune impulses of frequency equal to the auxiliary wave frequency and of width varying in proportion to the instantaneous amplitudes of said modulating wave.

2. A method of producing pulse time modulation which comprises the steps of phase modulating in accordance with a given modulating signal wave at least one of a pair of auxiliary and substantiallysquare-topped waves of likevi'requency and predetermined relatively fixed normal phase relation, and multiplicativeiy combining said auxiliary waves to produce a resultant wave comprising a series of constant amplitude impulses of frequency corresponding to the auxiliary wave frequency and of width varying in proportion to the instantaneous amplitudes of said modulating wave.

3. A method of producing pulse time modulation which comprises the steps of phase modulating in accordance with a modulating signal wave at least one of a pair of auxiliary sinusoidal waves of like frequency and predetermined fixed normal phase relation, multiplicatively combining said auxiliary waves, and rectifying an amplitude limiting the resultant wave to produce a series of substantially constant amplitude impulses of frequency equal to the auxiliary wave frequency and of width varying in proportion to the instantaneous amplitudes of said modulating wave.

4. A method of producing pulse-time modulation which comprises the steps of phase modulating in an opposite sense and in accordance with a given modulating signal wave a pair of auxiliary waves of like frequency and predetermined fixed normal phase relation, and mutually intermodulating thephase-modulated auxiliary waves to produce a series oi' substantially constant amplitude impulses of frequency equal to the auxiliary wave frequency and of width varying in proportion to the instantaneous amplitudes of said modulating wave.

5. A system for producing pulse-time modulated signals comprising means for producing a pair of auxiliary waves of like frequency and`l predetermined fixed normal phase relation, means for phase modulating at least one of said auxiliary waves in accordance with a given modulating signal wave, and means for mutually intermodulating said auxiliary waves to produce a resultant wave comprising a series of substantially constant amplitude impulses of frequency equal to the auxiliary wave frequency and of width varying in proportion to the instantaneous amplitudes of said signal wave.

6. A system for producing pulse-time modulated signals comprising means for producing ya pair of auxiliary waves of like frequency and of normally 90 phase relation, means for phase modulating at least one of said auxiliary waves in accordance with a given modulating signal wave, and meansV for mutually intermodulating said auxiliary waves to produce a resultant wave comprising a series of substantially constant amplitude impulses of frequency equal to the auxiliary wave frequency and of width varying in proportion to the instantaneous amplitudes of said signal wave.

7. `A system for producing pulse-time modulated signals comprising means for producing a pair of auxiliary waves of like frequency and normal 90 phase relation, means for phase modulating at least one of said auxiliary waves in accordance with a given modulating signal wave, means for mutually intermodulating said auxiliary waves and for amplitude limiting the resultant wave to produce a series of substantially constant amplitude impulses of frequency equal to the auxiliary wave frequency and of width varying in proportion to the instantaneous amplitudes of said signal wave.

8. A system for producing pulse-time modulated impulses comprising means for producing a pair of sinusoidal auxiliary waves of like frequency and normally phase relation, means for phase modulating at least one of said auxiliary waves in accordance with a given modulating signal wave. means for mutually intermodulating said auxiliary waves and amplitude limiting the resultant wave to produce a series ofsubstantially constant amplitude impulses of frequency equal to the auxiliary wave frequency and of width varying in proportion to the instantaneous amplitude of said signal wave.

9. A system for producing pulse-time modulated signal impulses comprising means for producing a pair of sinusoidal auxiliary waves of like frequency and normally 90 phase relation, means for phase modulating at least one of said auxiliary waves in accordance with a modulating signal Wave, means for multiplicativeiy combining said auxiliary waves. and further means for rectifying and amplitude limiting the resultant wave to produce a series of substantially constant amplitude impulses of frequency equal to the auxiliary wave frequency and of width varying in proportion to the instantaneous amplitudes of said signal wave.

10. A system for producing pulse-time modulated signal impulses comprising means for producing a pair of auxiliary waves of like frequency and predetermined relatively fixed phase relation. means for phase modulating both said auxiliary waves in accordance with a common modulating signal wave and in an opposite sense with respect to said fixed phase relation, and means for mutually intermodulating the phase modulated auxiliary waves to drive a resultant wave comprising a series of impulses of frequency equal to the auxiliary wave frequency and of width varying in proportion to the instantaneous amplitudes of said signal wave.

ll. A system for producing pulse-time modulated signal impulses comprising means for pro ducing a pair of auxiliary waves of like frequency and normally 90 phase relation, means for modulating in accordance with a given modulating signal wave both said auxiliary waves in an opposite sense with respect to said normal phase relation, and means for mutually intermodulating the phase modulated waves to produce a resultant wave, comprising a series of impulses of frequency equal to the auxiliary wave frequency and of width varying in proportion to the instantaneous amplitudes of said signal wave.

12. A system for producing pulse-time modulated signal impulses comprising means for producing a pair of sinusoidal auxiliary waves of like frequency and normally 90 phase relation, means for phase modulating in accordance with a given modulating signal wave both said auxiliary waves in an opposite sense with respect to said normal phase relation, means for mutually intermodulating the phase modulated auxiliary waves, and means for amplitude limiting the resultant wave to produce a series of substantially constant amplitude impulses of frequency equal to the auxiliary wave frequency and of width varying in proportion to the instantaneous amplitudes of said signal wave.

13. A system for producing pulse-time modulated signal impulses comprising means for producing a pair of substantially square topped auxiliary waves of like frequency and normally 90 phase relation, means for phase modulating'in accordance with a given modulating signal wave both said auxiliary waves in an opposite sense with respect to said normal phase relation. means for multiplicatively combining the phase modulated auxiliary waves, and means for rectifying and amplitude limiting the resultant wave to produce a series of substantially constant amplitude impulses 'of frequency equal to the auxiliary wave frequency and of width varying in proportion to Number o Number the instantaneous amplitudes of said signal wave. 15

GUsTAv GUANEILA. PAUL GTTINGER.

- REFERENCES CITED the UNITED STATES PATENTS Name Date Luck f.. July 13, 1937 v FOREIGN PATENTS Country Date Great Britain May 23, 1938 

